MAMMALS. 557 



which secrete the milk, with which the mother feeds her young, 

 and in being viviparous. Their skin, moreover, is not covered 

 with feathers, hut commonly with hair; only some have horny 

 scales or shields, which cover the back or also the feet and the 

 upper part of the head. 



The skeleton of mammals deserves, in the first place, our con- 

 sideration. The vertebral column is, with the exception of the 

 cetaceous animals, divided into the same regions as in man, viz. 

 the cervical, the dorsal, the lumbar, the sacral and the caudal. In 

 the cetacea, numerous vertebraj (in the porpess four or five and 

 forty) succeed to the dorsal vertebrae, and compose the tail, in 

 which the lumbar region cannot be distinguished from the sacrum. 

 Although the neck in the various species diff"ers greatly in length, 

 still it is found to consist in this class, with two or three excep- 

 tions, constantly of seven cervical vertebrae. The three-toed sloth 

 {Bradypus tridactylus) has nine cervical vertebras^; in Manatus 

 australis there are commonly six. Consequently the length of the 

 neck does not depend upon the number of its vertebr^^. In the 

 ungulate animals the length of the neck corresponds to that of the 

 fore-legs^. There are generally thirteen dorsal vertebr£e present, as 

 in most of the ruminants, and many rodents, in most species of the 

 genus Felts, in the dog, the fox, &c.; seldom only are there fewer 

 than twelve (eleven in some bats and in species oi Dasypus ; in one 

 species of this genus, according to Cuviee, there are only ten, 

 which appears to be a solitary exception). Just as rare is it 

 almost that there should be more than fifteen; the horse has 



' This remarkable exception was first noticed by Wiedemann, and by EoussEAU, 

 prosector of the Museum of the Garden of plants at Paris; see Ann. du Mus. V. 

 1804, p. '201. Bradypus torq^uatms has 8 cervical vertebrae; Bradypus didactylus has 

 the usual number (7). Although on the two lowest cervical vertebrae in Bradypus 

 tridactylus traces of ribs are found (see Th. Bell TraTisact. of the Zool. Soc. i. p. ri3), 

 yet these vertebra are not on this account to be considered as dorsal. (The transverse 

 processes of all the cervical vertebrae in the mammals and also in man have a mdimentary 

 rib on the anterior root.) 



2 The neck in man forms about one-seventh of the length of the whole verbetral 

 column ; in the giraffe three-sevenths. 



2 The elei^hant forms a remarkable exception to this rule, and the proboscis, which 

 performs the office of a hand (Aeistoteles Historla anim. Lib. 11. cap. i), com- 

 pensates the absence of a long neck, which would be ill able to support the heavy mass 

 of the head. Comp. CiCERO De natura Deor. Lib. 11. cap. 50. 



